This invention relates to a pilot aid for synthesizing a view of the world. When flying under Visual Flight Rules (VFR) the normal procedure for determining your position is to relate what you see out the window to the information on a paper map. During the day it can be difficult to determine your location because the desired landmark can be lost in the clutter of everything else. When flying at night you see mostly lights. When flying under Instrument Flight Rules (IFR) you must relate the information from various navigation aids to the information on a printed map. You must then interpret the map information in order to avoid flying into objects such as mountains and the like. An improvement in this situation came about when the global positioning system (GPS) became operational and available for civilian use. GPS directly provides map coordinates but you must still, however, interpret the map information. Systems have been developed which use GPS coordinates to access an electronic map which is presented on a display as a flat map. Systems have also been developed that present an apparent three-dimensional effect and some that present a mathematically correct texture-mapped three-dimensional projected display.
Both of these systems require a very large amount of storage for terrain data. The latter system also requires specialized hardware. Their high cost have prevented their widespread adoption by the avaiation community.
The 1984 patent to Taylor et al. (U.S. Pat. No. 4,445,118) shows the basic operation of the global positioning system (GPS).
The 1984 patent to Johnson et al. (U.S. Pat. No. 4,468,793) shows a receiver for receiving GPS signals.
The 1984 patent to Maher (U.S. Pat. No. 4,485,383) shows another receiver for receiving GPS signals.
The 1986 patent to Evans (U.S. Pat. No. 4,599,620) shows a method for determining the orientation of a moving object and producing roll, pitch, and yaw information.
The 1992 patent to Timothy et al. (U.S. Pat. No. 5,101,356) also shows a method for determining the orientation of a moving object and producing roll, pitch, and yaw information.
The 1993 patent to Ward et al. (U.S. Pat. No. 5,185,610) shows a method for determining the orientation of a moving object from a single GPS receiver and producing roll, pitch, and yaw information.
The 1992 patent to Fraughton et al. (U.S. Pat. No. 5,153,836) shows a navigation, surveillance, emergency location, and collision avoidance system and method whereby each craft determines its own position using LORAN or GPS and transmits it on a radio channel along with the craft's identification information. Each craft also receives the radio channel and thereby can determine the position and identification of other craft in the vicinity.
The 1992 patent to Beckwith et al. (U.S. Pat. No. 5,140,532) provides a topographical two-dimensional real-time display of the terrain over which the aircraft is passing, and a slope-shading technique incorporated into the system provides to the display an apparent three-dimensional effect similar to that provided by a relief map. This is accomplished by reading compressed terrain data from a cassette tape in a controlled manner based on the instantaneous geographical location of the aircraft as provided by the aircraft navigational computer system, reconstructing the compressed data by suitable processing and writing the reconstructed data into a scene memory with a north-up orientation. A read control circuit then controls the read-out of data from the scene memory with a heading-up orientation to provide a real-time display of the terrain over which the aircraft is passing. A symbol at the center of display position depicts the location of the aircraft with respect to the terrain, permitting the pilot to navigate the aircraft even under conditions of poor visibility. However, the display provided by this system is in the form of a moving map rather than a true perspective display of the terrain as it would appear to the pilot through the window of the aircraft.
The 1987 patent to Beckwith et al. (U.S. Pat. No. 4,660,157) is similar to U.S. Pat. No. 5,140,532. It also reads compressed terrain data from a cassette tape in a controlled manner based on the instantaneous geographical location of the aircraft as provided by the aircraft navigational computer system and reconstructs the compressed data by suitable processing and writing the reconstructed data into a scene memory. However, instead of providing a topographical two-dimensional display of the terrain over which the aircraft is passing and using a slope-shading technique to provide an apparent three-dimensional effect similar to that provided by a relief map as shown in the '532 patent, the '157 patent processes the data to provide a 3D perspective on the display. There are a number of differences between the '157 patent and the present invention:
1. The '157 Patent stores the map as a collection of terrain points with associated altitudes; the large amount of storage required by this approach requires that a tape be prepared for each mission. The present invention stores terrain data as a collection of polygons which results in a significant reduction of data base storage; larger geographic areas can be stored so that it it not necessary to generate a data base for each mission. PA1 2. The '157 Patent uses a tape cassette for data base storage; the long access time for tape storage makes it necessary to use a relatively large cache memory. The present invention uses a CD-ROM which permits random access to the data so that the requirements for cache storage are reduced. PA1 3. The '157 Patent accounts for the aircraft's heading by controlling the way the data is read out from the tape. Different heading angles result in the data being read from a different sequence of addresses. Since addresses exist only at discrete locations, the truncation of address locations causes an unavoidable change in the map shapes as the aircraft changes heading. The present invention stores terrain as polygons which are mathematically rotated as the aircraft changes attitude. The resolution is determined by number of bits used to represent the vertices of the polygons, not the number of storage addresses. PA1 4. The '157 accounts for the roll attitude of the aircraft by mathematically rotating the screen data after it is projected. The '157 Patent does not show the display being responsive to the pitch angle of the aircraft. In systems such as this the lack of fidelity is apparent to the user. People know what things are supposed to look like and how they are supposed to change perspective when they move. The present invention uses techniques that have long been used by the computer graphics industry to perform the mathematically correct transformation and projection. PA1 5. The '157 shows only a single cockpit display while one of the embodiments of the present invention shows a stereographic head-mounted display with a head sensor. The pilot is presented with a synthesized view of the world that is responsive to wherever the pilot looks; the view is not blocked by the cockpit or other aircraft structures. This embodiment is not anticipated by the '157 patent. PA1 1. The '638 Patent is for a digital map system only. The matter of how the location and attitude are selected is not addressed. The present invention uses a digital map as part of a system for presenting an aircraft pilot with a synthesized view of the world regardless of the actual visibility. PA1 2. The '638 Patent stores the map as a collection of terrain points with associated altitudes, thereby requiring a large amount of data storage. The terrain points are transformed into polygons during program run-time thereby adding to the processing burden. The present invention stores terrain data as a collection of polygons which results in a significant reduction of data base storage. PA1 3. The present invention also teaches the use of a stereographic head-mounted display with a head sensor. The pilot is presented with a synthesized view of the world that is responsive to wherever the pilot looks; the view is not blocked by the cockpit or other aircraft structures. This embodiment is not anticipated by the '638 patent.
The 1991 patent to Behensky et al. (U.S. Pat. No. 5,005,148) shows a driving simulator for a video game. The road and other terrain are produced by mathematically transforming a three-dimensional polygon data base.
The first sales brochure from Atari Games Corp. is for a coin-operated game (Hard Drivin') produced in 1989 and relates to the '148 patent. The terrain is represented by polygons in a three-dimensional space. Each polygon is transformed mathematically according to the position and orientation of the player. After being tested to determine whether it is visible and having the appropriate illumination function performed, it is clipped and projected onto the display screen. These operations are in general use by the computer graphics industry and are well known to those possessing ordinary skill in the art.
The second sales brochure from Atari Games Corp. is for a coin-operated game (Steel Talons) produced in 1991 and which also relates to the '148 patent and the use of polygons to represent terrain and other objects.
The 1993 patent to Dawson et al. (U.S. Pat. No. 5,179,638) shows a a method and apparatus for providing a texture mapped perspective view for digital map systems which includes a geometry engine that receives the elevation posts scanned from the cache memory by the shape address generator. A tiling engine is then used to transform the elevation posts into three-dimensional polygons. There are a number of differences between the '638 patent and the present invention:
The 1994 patent to Hamilton et al. (U.S. Pat. No. 5,296,854) shows a helicopter virtual display system in which the structual outlines corresponding to structual members forming the canopy structure are added to the head-up display in order to replace the canopy structure clues used by pilots which would otherwise be lost by the use of the head-up display.
The 1994 patent to Lewins (U.S. Pat. No. 5,302,964) shows a head-up display for an aircraft and incorporates a cathode-ray tube image generator with a digital look-up table for distortion correction. An optical system projects an image formed on the CRT screen onto a holographic mirror combiner which is transparent to the pilot's direct view through the aircraft windshield.
The sales brochure from the Polhemus company shows the commercial availability of a position and orientation sensor which can be used on a head-mounted display.
The article from EDN magazine, Jan. 7, 1993, pages 31-42, entitled "System revolutionizes surveying and navigation" is an overview of how the global positioning system (GPS) works and lists several manufacturers of commercially available receivers. The article also mentions several applications such as the use by geologists to monitor fault lines, by oil companies for off-shore oil explorations, for keeping track of lower-orbit satellites, by fleet vehicle operators to keep track of their fleet, for crop sprayers to spread fertilizer and pesticides more efficiently, and for in-car systems to display maps for automotive navigation.
The section from "Aviator's Guide to GPS" presents a history of the GPS program.
The sales brochure from Megellan Systems Corp. is for commercially available equipment comprising a GPS receiver with a moving map display. The map that is displayed is a flat map.
The sales brochure from Trimble Navigation is for a commercially available GPS receiver.
The sales brochure from the U.S. Geological survey shows the availability of Digital Elevation Models for all of the United States and its territories.
The second sales brochure from the U.S. Geological survey shows the availability of Digital Line Graph Models for all of the United States and its territories. The data includes: political and administrative boundaries; hydrography consisting of all flowing water, standing water, and wetlands; major transportation systems consisting of roads and trails, railroads, pipelines, transmission lines, and airports; and significant manmade structures.
The Washington Sectional Aeronautical Chart is a paper map published by the U.S. Department of Commerce, National Oceanic and Atmospheric Administration that shows the complexity of the information that an aircraft pilot needs in order to fly in the area covered by the map. The other areas of the U.S. are covered by similar maps.
The sales brochure from Jeppesen Sanderson shows that the company makes its navigation data base available in computer readable form.
Accordingly, several objects and advantages of my invention are to provide a system that produces a mathematically correct three-dimensional projected view of the terrain while reducing the amount of storage required for the data base and which can be accomplished by using standard commercially available components. The invention can be used as a real-time inflight aid or it can be used to preview a flight, or it can be used to replay and review a previous flight.
Further objects and advantages of my invention will become apparant from a consideration of the drawings and ensuing description.